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Sexual dimorphism is common in many extant animals, but it is difficult to demonstrate in fossil species. Working with material from the Late Cretaceous of the U.S. Coastal Plain, we herein analyze sexual dimorphism in ostracodes from the superfamily Cytheroidea, a group whose extant members have males that are relatively more elongate than females. We digitized outlines of more than 6000 individual ostracode valves or carapaces, extracted size (area) and shape (length-to-height ratio) information, and used finite mixture models to assess hypotheses of sexual dimorphism. Male and female clusters can be discerned in nearly all populations with sufficient data, resulting in estimates of size and shape dimorphism for 142 populations across 106 species; an additional nine samples are interpreted to consist only of females. Dimorphism patterns varied across taxa, especially for body size: males range from 30% larger to 20% smaller than females. Magnitudes of sexual dimorphism are generally stable within species across time and space; we can demonstrate substantial evolutionary changes in dimorphism in only one species, Haplocytheridea renfroensis. Several lines of evidence indicate that patterns of sexual dimorphism in these ostracodes reflect male investment in reproduction, suggesting that this study system has the potential to capture variation in sexual selection through the fossil record.
All behavior occurs within the theater of evolution and hence it would be remiss to ignore evolutionary forces and outcomes when considering how behavior and conservation interact with each other. This is particularly pertinent as conservation outcomes can play out over a long time period, increasing the probability that conservation of biota will be affected by evolutionary forces and the evolutionary responses of organisms and communities to such forces.
To interweave evolutionary thinking into an approach to conservation behavior I will first, briefly, review how evolution works and offer a primer on micro-evolutionary forces. From there I will build evidence for how human alteration of the environment influences evolutionary forces and biological outcomes. Importantly, I will also layer-on a view of how macro-evolutionary patterns relate to conservation outcomes over long time periods, framed in the context of modern threats to biodiversity.
This evolutionary foundation lets me argue that behavior can lead evolution and not just be the outcome of evolutionary forces. Hence, behavioral mechanisms can alter evolutionary trajectories over a surprisingly short time period and affect conservation outcomes; a view not commonly held even among evolutionary biologists. This view will be integrated back to this book's initial framework of how behavior and conservation intersect with each other, revising the Berger-Tal et al. (2011) model to explicitly include micro- and macro-evolutionary forces, patterns and outcomes.
A BRIEF PRIMER ON MICRO-EVOLUTIONARY FORCES
Evolution is classically defined as the change in allele frequencies in a population over time (Maynard Smith & Szathmáry 1995, Stearns & Hoekstra 2005, Swaddle 2010). What this definition does not readily admit to is that this is perhaps an overly gene-centric definition of micro-evolution, yet our concept of evolution is much larger than tracking gene variants over time. Evolution is really the change in heritable variation in populations (defined broadly, as I will explain later when tackling macro-evolutionary topics) over time. By heritable variation I mean differences in a population that can be passed on from one generation to another, which can occur by many mechanisms including traditional genetic inheritance, epigenetic processes, parental effects, and some would argue by cultural inheritance also.
Although phylogenetic systematics is used to reconstruct evolutionar 123y relationships, undergraduates have a difficult time mastering its fundamental concepts. Because it is a key part of the mainstream professional thinking, we explored in what ways students misread cladograms, which are the abstract and synthetic diagrams of phylogenetic systematics. We developed a questionnaire to examine the following four hypotheses as to how introductory college-level students (n=51) read cladograms: 1) students read cladograms correctly; 2) students infer that proximity of tips equals relatedness; 3) students read cladograms as they might an evolutionary tree, reading left to right as primitive to more advanced, and perceiving organisms as branching off; and 4) students infer ancestors at the nodes. Most responses fell into one of the four hypotheses, with 55% following the scientific (‘correct’) hypothesis. Most students answered between six and eight of the ten questions correctly. Slightly more than half of the students generally followed the scientific hypothesis, while others applied both the scientific and proximity (hypothesis 2, above) hypotheses together. A few students followed the primitive hypothesis (hypothesis 3, above). Our recommendation is that instructors address discrepancies between the scientific and proximity hypotheses in particular. For undergraduates, generally, cladograms require focused teaching, explanation, and active-learning approaches to be successfully used to teach phylogenetic systematics.
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